Translation:At the top of the mountain, the sky was cloudy.
There is also the matter that "mountaintop" and "top of the mountain", while referring to the same thing, are still different. Likewise, Japanese has words more akin to "mountaintop", but 「山の上」 translates to "top of the mountain".
I really wish people would stop thinking that any synonym can conveniently replace any other without so much as any change in meaning at all. Synonyms aren't always truly equal.
Well, english wise, but the point is to translate the sentences as close as possible to the original.
In english people would understand the sky was cloudy, but it can litterally mean the mountain itself is cloudy - cloud-like, it's not a proper use, true, but either way that's not the point.
to make this distinction more clear, in the case of looking at a mountain, i would say "above the mountain" to refer to anything but the most localized of atmospheric events, but when i was talking about hiking I'd say "top of the mountain" to describe anything i experienced while i was at the top of the mountain.
does ~の上 have the same effect on things as ~の前, or are they differently applied: as in, "the top face of..." versus "the front space of..."
to rephrase this, can you use ~の前 to describe a stain on the front of someone's clothing, or can you use ~の上 to describe a pull-chain above them, and, in either case, how would you do that?
I understood from this lesson that くもって could be more appropriately interpreted as “BECOMING cloudy” so the particle で would indicate an action that was taking place at the top of the mountain. I am a beginner so you should certainly take this with a grain of salt; I hope someone can confirm or correct.
With verbs of state the progressive construction doesn't mean becoming: くもっています - it is cloudy, くもっていました - it was cloudy. Some other verbs like this that come up in this course are 痩せる (やせる), which means to lose weight, but 痩せています - to be thin, and 知る (しる) - to know, but 知っています is how you would say "I know" (I'm in a state of knowing).